1. Field of the Invention
The present invention relates to: an amine compound; an electrophotographic photoconductor including the amine compound; and an image forming method, an image forming apparatus and a process cartridge using the electrophotographic photoconductor.
2. Description of the Related Art
In recent years, development of an information-processing system device using an electrophotographic method is remarkable. In particular, a laser printer and a digital copier, which convert information to digital signals and carry out information recording with light, have improved significantly in terms of their print quality and reliability. Further, through combination with high-speed technology, they have been applied to a laser printer or a digital copier with which a full-color printing is possible. From such a background, to have both high image quality and high durability as functions required for a photoconductor has become an especially important issue.
As a photoconductor used for these electrophotographic laser printer and digital copier, a photoconductor with an organic photosensitive material (OPC) is widely used in general for reasons such as cost, productivity and free of pollution. In addition, a layer configuration of the OPC photoconductor is divided into a single-layer structure and a functionally separated laminated structure. For example, a PVK-TNF charge-transfer complex photoconductor as a first practical OPC had the former single-layer structure. Meanwhile, a PVK/a-Se multilayer photoconductor was invented independently by Hayashi and Regensburger in 1968, and later, a multilayer photoconductor was presented by Melz et al. in 1977 and by Schlosser in 1978, where the photoconductive layer, namely an organic pigment dispersion layer and an organic low-molecular-weight dispersed polymer layer, was composed totally of an organic material. These are also called as a functionally separated laminated photoconductor because of a concept that it is composed of a charge generation layer (CGL) which absorbs light and generate charge and a charge transport layer (CTL) which injects and transports the charge generated by the CGL and neutralizes a surface charge. By development of this functionally separated laminated photoconductor, sensitivity and durability have drastically improved compared to a single-layer photoconductor. Also, since individual molecular designs of materials having different functions, namely a charge generation material (CGM) and a charge transport material (CTM), are possible, choice of these materials has greatly increased. Because of these reasons, the functionally separated laminated photoconductor is a major layer configuration of the present OPC photoconductor.
A mechanism of an electrostatic latent image formation in a functionally separated photoconductor is as follows. A light is irradiated to a charged photoconductor, the light passes a charge transport layer and is absorbed by a charge generation material in a charge generation layer, and charge is generated. The charge generated thereby is injected into the charge transport layer at an interface between the charge generation layer and the charge transport layer, it is further transferred within the charge transport layer by means of an electric field, and it neutralize the surface charge of the photoconductor. Thereby, an electrostatic latent image is formed.
However, an organic photoconductor is subjected to severe film chipping due to repeated use. As the film chipping in the photoconductive layer progresses, background smear, image density decrease or image degradation caused by decrease in charge potential and degradation of light sensitivity of the photoconductor and scratches on a surface of the photoconductor tend to progress. Accordingly, abrasion resistance of the organic photoconductor has been conventionally pointed out as a big issue. Further, in recent years, high durability of a photoconductor has been more important than ever due to reduction in diameter of the photoconductor due to speeding up of an electrophotographic device or downsizing of an apparatus.
As a method for achieving improved abrasion resistance of a photoconductor, methods of lubricating, curing or incorporating a filler to a photoconductive layer, or a method of using a polymeric charge transport material instead of a low-molecular charge transport material (CTM) molecule dispersed polymer layer are widely known. However, suppression of chipping in a photoconductive layer by these methods causes a new problem. That is, it has been known that ozone, NOx, or other oxidizing substances produced by repeated use or the surrounding environment are adsorbed on a surface of the photoconductive layer, which leads to low resistivity of an outermost surface depending on the repeated use and the use environment, causing problems such as image deletion (image blurring). Conventionally, this blur-generating substance is chipped off along with the photoconductive layer, and the problem has been avoided to some degree. However, as described above, a new technique must be employed to meet recent demands for higher resolution and higher durability. There is a method of carrying a heater on a photoconductor to evaporate a blurring substance as one of the methods to reduce effects thereof, but this method is a big obstacle for downsizing of an apparatus and reduction of energy consumption. Also, an additive such as antioxidant is an effective method, but an ordinary additive does not have photoconductivity. Thus, addition of a large amount to a photoconductive layer causes problems of electrophotographic characteristics such as low sensitivity and increased residual potential.
As above, the electrophotographic photoconductor imparted with high wear resistance, or less chipping because of process design around the photoconductor cannot avoid effects on image quality such as occurrence of image blurring and decreased resolution as side effects, and it has been considered difficult to obtain both high durability and high image quality. High resistance is preferable for suppressing occurrence of image blurring, and low resistance is preferable for suppressing elevation of residual potential. These are in a trade-off relation, which makes it difficult to solve the problems.
Meanwhile, in Japanese Patent (JP-B) No. 4226749, an aromatic compound having a dialkylamino group as an acid scavenger of a photoconductor is disclosed. Also, diamine compounds are disclosed in Japanese Patent Applications Laid-Open (JP-A) No. 5-158258 and JP-A No. 2009-14851. These compounds are described to be effective for image quality after repeated use of a photoconductor and to solve the problems of image deletion (image blurring) by the blur generating substance such as oxidizing gas. However, due to low charge transportability, it is difficult to respond to the requests for high sensitivity and speeding up, and accordingly, there is a limit in an amount of addition.
Further, it is reported that stilbene compounds including a dialkylamino group disclosed in JP-A No. 60-196768, JP-B No. 2884353, etc. are effective for image blurring due to an oxidizing gas ([Itami et al., Konica Technical Report, Vol. 13, p. 37, 2000]).
However, since the stilbene compounds include a dialkylamino group as a substituent having a strong mesomeric effect (+M effect) at a resonance region of a triarylamine structure as a charge transport site, an ionization potential value as a whole is abnormally small. Therefore, charge retention capacity of a photoconductive layer which uses it solely as a charge transport material is initially poor or degrades severely due to repeated use, and it has a fatal defect that practical use is extremely difficult. Also, even though it is mixed with other charge transport materials as in the present invention, the stilbene compound has an ionization potential value considerably smaller than those materials. The stilbene compound becomes a hole trap site of transferred charge, and a resultant electrophotographic photoconductor has defects of significantly low sensitivity and large residual potential.
Also, diamine compounds effective for suppressing image degradation due to NOx, etc. are disclosed in JP-B No. 4101676 and JP-B No. 3949550. Reduction of sensitivity thereof is relatively small, but it is considered insufficient because it has a problem of decreased resolution due to cyclic fatigue.
Further, an amine compound in which a dialkylamino group is directly bound to a triarylamine structure is disclosed in JP-B No. 3996490. However, similarly to the stilbene compounds, a resultant electrophotographic photoconductor has a defect of significantly low sensitivity and high residual potential.